Benzene oxides synthesis

Numerous substituted 3-oxaquadricyclanes (3-oxatetracyclo[3.2.0.02 7.04,6]heptanes) undergo thermal isomerization to oxepins24 30,121 126 which are often in equilibrium with the corresponding benzene oxides.127 128 The synthesis of the 3-oxaquadricyclanes usually starts with... 

Synthesis By Ring Enlargement from. vy/i-Benzene Oxide Imines... 

Oxepin is in equilibrium with benzene oxide by a [3,3]-sigmatropic shift. Advantage has been taken of this equilibrium to develop a short synthesis of barrelene. Outline a way that this could be done. 

A large number of studies have investigated the metabolism of benzene per se or in relation to toxification and, particularly, myelotoxicity. Most evidence shows that benzene oxide (10.1, Fig. 10.8) is not the ultimate toxic species, as was initially believed. Indeed, phenol and quinone metabolites of benzene are more active in forming adducts with macromolecular nucleophiles and eliciting cellular toxicity. For example, the efficacy of benzene metabolites (see Fig. 10.8) to inhibit DNA synthesis in a mouse lymphoma cell line decreased in the order benzoquinone (10.17) > hydroquinone (10.16)... 

Table 10.6 shows the catalytic performances of the selective benzene oxidation on the zeolite-supported Re catalysts under steady-state reaction conditions [107]. Catalyhc activity and selectivity largely depended on the types of zeolites and the preparation methods. The Re catalysts prepared by CVD of MTO exhibited higher catalyhc achvity and phenol selechvity than those prepared by the convenhonal impregnation method as supports (Table 10.6). Physical mixing of MTO with the supports provided poor phenol synthesis.

O ) By formation of seven-from three-membered rings This is the most widely used synthetic route to monocyclic oxepins. The key step in the synthesis of oxepin-benzene oxide (7) is the dehydrohalogenation of a dibromoepoxide precursor (64AG(E)S10). Since the benzene oxide valence tautomer is formed initially the valence tautomerization of the latter to oxepin (equation 51) may be considered as a ring expansion reaction. 

Dehydrohalogenation has also been utilized in the synthesis of 1-acetyl-benzene oxide (102) from the dibromo compound 103.8... 

The coexistence of NH3 is indispensable for selective benzene oxidation. Neither benzene oxidation nor combustion proceeded in the absence of NH3 (Table 2.5). Fe/ZSM-5 has been reported to be active and selective for phenol synthesis from benzene using N20 as an oxidant [97], but selective benzene oxidation did not proceed with N20 instead of 02. The addition of H20 to the system gave no positive effects on the catalytic performance, either. In addition, other amine compounds such as pyridine and isopropyl amine did not produce phenol. The phenol formation rate and selectivity increased with increasing NH3 pressure because the coexisting NH3 produces active Re clusters, as described below, and reached maximum conversion and selectivity at a partial pressure of NH3 of around 35—42kPa. 

The wide range of monosubstituted benzene oxides that have been synthesized using halogenoepoxide or related routes is illustrated by the examples given in Figure 3. This general route (Figure 4) has been used in the synthesis of mono-... 

Figure 3. Structures of synthesized monosubstituted benzene oxides. References to each synthesis are superscripted.

Figures. Established modifications of a substituent X prior to synthesis of 1-substituted benzene oxides. See Figure 3 for product arene oxides.

Arene oxides 42 and 49 were obtained as minor products by an unusual thermal isomerization of the photooxide of 3-diphenylisobenzofuran. Although the thermal isomerization reaction of 3-oxaquadricyclane has been used in the synthesis of benzene oxide 1, this route to benzene oxides was initially limited to specifically substituted derivatives owing to the unavailability of the unsubstituted 7-oxanorbornadiene. Thus most of the substituted arene oxides prepared by this route contained electron-withdrawing substituents X [X = —CF3 (77), —COaMe (76, 86, 88-92, 94), and —C02Et (93)] which increased their thermal stability. 

The halogenoepoxide route to benzene oxides has been used in the synthesis of arene oxides 11, 13, 4116,117 21/ 1 25, and 26 as well as the azaarene oxide 140. The major problem of this synthetic route to non-K-region arene oxides is typified by the results obtained by early attempts to prepare 13 and 15. Thus, the tetrahydroepoxide and bromoepoxide intermediates were highly unstable under the required reaction conditions and yielded a highly impure... 

The epoxidation reaction of arene oxide-oxepins has been encountered in the formation of the arene dioxides of naphthalene and anthracene rings A similar approach to the synthesis of epoxides of benzene oxide-oxepin using a peroxyacid oxidant, however, was unsuccessful (Z,Z)-muconaldehyde was isolated presumably via an oxepin-epoxide intermediate. The disubstituted benzene... 

Oxepins and their bicyclic valence tautomers, arene oxides are discussed in <95CHE(42)197>. Particularly noteworthy is the synthesis of a stable benzene oxide (63) which surprisingly shows little tendency to isomerize to the corresponding oxepin (64) in spite of the expectation that the fluorines would greatly destabilize the three-membered ring in the bicyclic structure (63) (Scheme 10) <90JA6715>. 

SCHEME 75. Oxidative fluorination of p-substituted phenols withbis(trifluoroacetoxy)benzenes and synthesis of hydroindolenones... 

A synthesis protocol of porous zirconia catalyst support, through a neutral Ci3(EO)6-Zr(OC3H7)4 assembly pathway has been developed. Our studies evidenced the role played by the surfactant. It has also been observed that the increase of hydrothermal treatment time and temperature have a benefical effect on tailoring the pore sizes. The synthesized materials will be used in preparation of Au / ZrOz, Au / VO / ZrOz catalysts, which will be tested in the benzene oxidation reaction. Thermogravimetric analysis shows that the recovered zirconia present a relatively low thermal stability. Then the structure collapses due to the crystallization to more stable tetragonal and monoclinic phase. 

Relatively few significant papers appeared on oxepine systems or fused derivatives. Rearrangement processes were commonly involved in their synthesis. For example, treatment of 89 with n-BuLi and then methanesulfonyl chloride afforded the oxepine 90 as a dark red solid in good yield via rearrangement of the intermediate substituted benzene oxide derivative <05TL3221>. 

In the case of benzene, one possible species absorbing in the region of 275 m/Lt is phenol. By measuring the absorption of phenol vapor in one atm. of air at 24 °C. in a Cary spectrophotometer, we found the absorption coefficient to be 4-5 X 103M 1 cm."1 at 275.7 m/ however, the absorption peak at 275.7 was very sharp, the absorption reaching zero by about 280 m/. We do not know how much the 50 fold increase in pressure used in the pulsed-radiolysis experiment would affect the width of the absorption, but it is very unlikely that phenol is the only absorbing species. In a recent study (10) on the synthesis of benzene oxide (A) in isooctane solution, this compound was found to have a maximum absorption at 271 m/x, and to be in equilibrium with oxepin (B), with a maximum at 305 m/x. 

Relatively few reports appeared on oxepine systems in 2004. The preparation of benzene oxide/oxepine has been observed in the gas phase reaction of benzene with oxygen atoms. Further reaction of this product with these atoms then gave a mixture of products including a compound thought to be oxepin-4,5-epoxide or oxepin-2,3-epoxide <04MI391>. Of relevance to this work is the report of the first observation of a 4,5-benzoxepin-2,3-oxide by H NMR <04TL4789>. Other fused systems have been of interest. The synthesis of a novel bicyclic oxepinopyrimidine 62 has been described. Acetylation of the alcohol 60 afforded the acetate derivative 61 which was then cyclised to the oxepine derivative 62 plus 63 on treatment with concentrated HCl <04H(63)2523>. 

The synthesis of monocyclic oxepins starts from 3,4-dibromo-7-oxabicyclo[4.1.0]heptanes 12, which are readily accessible from cyclohexa-1,4-dienes by monoepoxidation providing 13, followed by bromine addition to the remaining double bond. A double dehydrobromination of 12 with methoxide or DBU yields the benzene oxide/oxepin ... 

Synthesis of benzene oxides, which are in equilibrium with oxepines, is one of the most valuable methods for their preparation. As an example of its potential, a rather simple three-step synthesis of 2,7-diphenyloxepin can be given (Scheme 19) <86JOC2784>. The equilibrium of the latter with the respective benzene oxide is shifted to the side of oxepin, but treatment of the product with trifluoro-acetic acid quantitatively gives 2,6-diphenylphenol. 

Styrene is obtained almost exclusively by dehydrogenation of ethyl benzene, and in small quantities by the dehydration of a-methyl benzyl alcohol, the by-product of the propylene oxide synthesis from propylene and a-methyl benzyl hydroperoxide. Styrene can be polymerized free radically, cationically, anionically, and with Ziegler-Natta catalysts. Only the free radical polymerizations have commercial significance. 

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